Piezoelectric transducer for destruction of concretions inside the body

Abstract

A piezoelectric transducer for destruction of concretions inside the body. The transducer essentially comprises a spheroidal cap having piezoelectric ceramic elements situated at its radially inner front side. To prevent overpressure pulses radiated at the front side of the transducer being followed by underpressure pulse reflected from the rear side of the cap, the cap is produced from metal, preferably from a copper alloy. The impact wave resistances of the cap metal and of the ceramic material should largely correspond. Furthermore, the rear-side surface of the rear wall of the cap is so shaped geometrically and/or provided with a coating, that the sonic waves reflected therefrom are no longer focussed.

We claim: 
     
       1. In a piezoelectric transducer for destruction of concretions inside a body, said transducer comprising a cap having an inner surface with a partially-spherical curvature with a given radius from a point, said cap having a back surface, a plurality of piezoelectric ceramic elements for producing sonic pulses being mounted on the inner surface to form a mosaic of elements with the output of the sonic pulses from said mosaic of elements being focussed at said point, the improvements comprising the cap being of a metal with an wave impact resistance of the metal corresponding at least substantially to the wave impact resistance of the material of the ceramic elements, and the cap having means for scattering sonic pulses entering into the cap from the elements to prevent the back surface of the cap from reflecting a focussed wave of sonic pulses at said point. 
     
     
       2. In a piezoelectric transducer according to claim 1, wherein the cap is made from a copper alloy. 
     
     
       3. In a piezoelectric transducer according to claim 1, wherein the means for scattering incldues said back surface of the cap having irregular recesses therein. 
     
     
       4. In a piezoelectric transducer according to claim 3, wherein said back surface is coated with an insulating and sound-absorbing material and wherein said irregular recesses cause a uniform transition of the impact wave resistance into said sound-absorbing material. 
     
     
       5. In a piezoelectric transducer according to claim 1, wherein the means for scattering include the back surface of the cap being divided into curved partial surfaces having curvatures which are assymetric relative to an axis of the cap, said curved partial surfaces having radii of curvature which differs substantially from the radius of curvature of the inner surface of the cap. 
     
     
       6. In a piezoelectric transducer according to claim 5, wherein said partial surfaces have irregular recesses. 
     
     
       7. In a piezoelectric transducer according to claim 6, wherein the partial surfaces of the back surface are coated with an insulating and sound-absorbing material.